In a dynamic random access memory DRAM chip, the peripheral devices used to filter out power-supply noise are banks (hundreds) of capacitors connected across the power supply terminals. In case of capacitor dielectric failure, an excessive current flows (20-40 ma) in the capacitor which can create a high chip standby current or, in a worst case, cause latch-up. Latch-up has the effect of shorting the voltage terminals resulting in chip self-destruction or system failure with the requirement to power down.
It is, therefore, desirable to protect the chip by a fuse means in series with the device or component. It is also desirable to utilize a minimum area device, i.e., a submicron width fuse that lies in a planar surface with the protected part and that can interrupt at milliamp levels.
Metal fuses in this submicron width range cannot provide adequate protection for noise-suppression capacitors since they require currents of over 100 milliamps to interrupt the circuit.
Prior art in this field includes U.S. Pat. No. 5,019,532 issued to Kaya on May 28, 1991, which discloses a small fuse for use in a programmable read-only memory (PROM). The actual small fuse consists of a dielectric consisting of a composite layer of a thin nitride deposited over a thin oxide layer.
U.S. Pat. No. 4,647,340 issued to Szluk et al. on Mar. 3, 1987 also discloses a fuse formed of a selectively thinned oxide which degenerates to a resistance on application of the high voltage V.sub.pp when programming the chip.
U.S. Pat. No. 5,059,555 issued to Iranmanesh et al. on Oct. 22, 1991 discloses another vertical configuration fuse used in programming PROMs and programmable logic arrays (PLA). The vertical device is fabricated in the same structure as a polysilicon transistor. After programming, the fuse resistance is less than 150 ohms.
U.S. Pat. No. 4,598,462 issued to Chandrasekhar on Jul. 8, 1986 discloses a method and device for making a semiconductor where some of the elements have fuses formed adjacent and above the protected elements. The fuse element is a layer of silicon nitride covered by polysilicon and then covered by a platinum layer, forming a platinum silicide fuse after heating to 650.degree. C. U.S. Pat. No. 4,518,981 issued to Schlupp on May 21, 1985 discloses a combined Schottky diode and fuse for programming a PROM. The fuse is activated by a high voltage and is constructed from a platinum silicide.